Positive displacement-type hammer drill



July 30, 1957 E. ALMom 2,800,884

POSITIVE DISPLACEMENT-TYPE HAMMER DRILL Filed Feb. 24, 1956 2Sheets-Sheet 1 INVENTOR.

///$ ATTORNEY July 30, 1957 E. A. MORI POSITIVE DISPLACEMENT-TYPE HAMMERDRILL 2 Sheets-Sheet 2 Filed Feb. 24, 1956 ka zv UV AK INVENTOR.

52/1/6157 A. MQQ/ w m m w Ms ATTOQIYEI/ PQSETIVE DISPLACEMENT-TYPEHARHIVIER DRILL Ernest A. Moi-i, Pittsburgh, Pa., assignor to GulfResearch & Development Company, Pittsburgh, Pa, 2 corporation ofDelaware Applicatien February 24, 1956, Serial No. 567,751

9 Claims. (Cl. 12115) This invention relates to well drills and moreparticularly to a well drill combining the advantageous features ofrotary and positive displacement type percussion drill mechanisms.

One of the advantages of my invention is the provision of a hammer drillin which the two reciprocating hammers are the only moving parts. Thesereciprocatng parts may be made of comparable weight so as to impartseparate percussive blows of equal force. Both hammers of my inventionstrike the anvil directly and at different times with approximately thesame force.

Another advantage of my invention is the provision of a hammer drill inwhich each of the hammers acts as a valving element as well as impartinga useful percussive blow at the end of its downward travel. In myinvention ports for fluid passage are incorporated in the outer hammer,and the central passage of the inner hammer also acts intermittently asa passage for fluid, so that both hammers function as valving elements.

A further advantage of my invention is in providing a fluid operatedmechanism for delivering percussive blows to the drill bit withoutinterrupting the downward flow of fluid through the drill pipe and bit.My invention provides for continuous flow of fluid through the mechanismin that the fluid flow is never completely shut off by the hammers atany point in their reciprocating motion. My invention is a positivedisplacement-type drill and there are no openings or passages thatpermit fluid to bypass the unit during the operating cycle so that allfluid supplied to the unit is utilized except for a minimal amount ofleakage. Conversely since all of the flow supplied to the unit iseffective, the drill will operate with a minimum of flow.

Still another advantage of my invention is the provision of a hammerdrill in which both hammers are hydraulically driven in both directionsso that the force and frequency of the blows applied to the anvil by thehammers are direct functions of the flow rate of fluid through the drillmechanism.

Because of the fact that both hammers of my invention are hydraulicallydriven in both directions and the operation of the mechanism is nottherefore dependent on the force of gravity aided by spring action tomove the hammers downward, my drill is not limited to operation in avertical position such as is normally used in well drilling but willfunction in any plane inclined to the vertical or in a horizontalposition or in an inverted position.

A further advantage of my invention is the provision of a percussiondrill which will operate with relatively light weight on the formationbeing drilled.

Another advantage of my invention is the provision of a positivedisplacement-type hammer drill in which both hammers operatecontinuously. When either of the hammers strikes the anvil or hasreached its maximum elevation on the up-stroke and is momentarilystopped, the other hammer is in motion. In this manner intermittentflow, which is a principal factor in causing presnited States Patent2,800,884 Patented July 30, 1957 sure surges, is prevented, so thatfluid pressure surges caused by the hammer portion of the drillmechanism are practically eliminated. Furthermore, the upward movementof both hammers is arrested by hydraulic cushion action which is alsoeffective in preventing hydraulic hammer and consequent fluid pressuresurges.

A still further advantage of my invention is the provision of a hammerdrill of simplified design such that all parts may be made large, heavyand strong whereby breakage of parts and shutdown of the drill forrepairs is substantially eliminated.

My invention is illustrated in the drawings accompanying thisspecification and forming a part thereof and in which:

Figure 1 is a longitudinal section taken through the upper portion of apreferred embodiment of my drill;

Figure 2 is a longitudinal section taken through the lower portion ofthe drill of Figure 1 showing the drill bit attached thereto; and

Figures 3 to 9 inclusive are diagrammatic representations illustratingvarious phases during the operation of my drill.

Reference is made to the drawings in which like numerals indicate thesame element in the various views and diagrams. In Figure 1 adaptor 1serves to connect the drill assembly with the drill string (not shown),the latter having a central passage as is conventional for supplyingdrilling fluid. Adaptor 1 is provided with a central passage 2 for thepurpose of supplying drilling fluid under pressure to the drillmechanism. Adaptor 1 is screwed into the drill housing 5 by threads 4.Immediately below adaptor 1 and fitting snugly within housing 5 is ashort circular section of flat spacer spring 6 provided wit-h a space 7between spirals which permits limited compression of the spring. Thepurpose of this spring will be described later.

Below spacer spring 6 is positioned a manifold 8 which fits snuglywithin housing 5, against the lower surface of spring 6. The upperportion of manifold 8 is hollow to receive the downward flow of fluidfrom passage 2 of the adaptor. Below the upper end of manifold 8 is aportion of reduced external diameter as at 9 which is provided at thispoint with a series of ports 10 spaced about its circumference, throughwhich the downward flow fluid is laterally diverted by the solid lowerportion 11 of manifold 8. The solid lower portion 11 of manifold 8 fitssnugly within cylinder 13, being sealed to the inside of cylinder 13 byO-ring 12 which is seated in a groove 12a. Cylinder 13 is concentricallypositioned within housing 5 by lugs 14 of which there are three or morecircumferentially spaced therearound and which may be welded to theouter surface of cylinder 13 to serve as guides, sliding freely on theinner surface of housing 5 during assembly or adjustment of the partsbut allowing circulation of fluid between lugs. Manifold 8 is held inplace abutting the lower surface of spacer spring 6 by two parallel pins15 and 15a which are inserted through the wall of cylinder 13 from theoutside thereof and which engage slots 16 and 16a in manifold 8. Bothends of pins 15 and 15a extend beyond the cylinder sutficiently so thathousing 5 will prevent them from being displaced while the assembly isinside of the housing. The pins 15 and 15a are easily removed when theinner assembly is withdrawn from the housing 5 if repair or replacementof parts becomes necessary. Slots 16 and 16a are of suflicientlongitudinal dimension to permit limited longitudinal movement ofmanifold 8, the purpose of which will be explained later. v

Abutting the lower surface of manifold 8 and fitting snugly within thecylinder 13 is a solid cylindrical member 17 provided with a downwardlyprojecting central boss V bossl8 and the hydraulic fluid, acts as adash-pot to hydraulically cushion and terminate the upward'movement ofthe inner hammer when it approaches the limit of its upward travel. Thelower end of annular member 19 hasa portion of reduced external diameteras at 20 and positioned partly within the annular space defined betweenthe portion of reduced diameter 20 and cylinder 13 is a small annularmember 22. The small annular member 22 fits snugly within cylinder 13and extends below the lowermost part of the portion of reduced externaldiameter 20 of annular member 19. The lower end of the small annularmember 22 fits against a shoul der 25 in the inner surface of cylinder13. At its lower end' cylinder 13 in turn abuts liner 26 which also fitsclosely within housing 5. Liner 26 at its lower end fits against lowervalve ring 27 and below lower valve ring 27 is still another liner 28,each of these members fitting closely within housing 5. v The lower endof housing is threaded as at 30 for a bushing 29 which has a smallerinternal diameter than housing 5 so that the various liners, valve ring,etc. are firmly clamped between shoulder 31 of bushing 29 and shoulder 3of adaptor 1 when the bushing 29 is screwed up tightly into housing 5.Thus bushing 29 holds in place, within housing 5, liner 28, lower valvering 27, liner 26, cylinder 13 and cylindrical member 17, annularmembers 19 and 22, manifold 8 and spacer spring 6, the latter abuttingagainst shoulder 3 of adaptor 1. The purpose ofspacer spring 6 withspace 7 for compression thereof and the longitudinal space in slots 16and 16a, permitting limited longitudinal movement of pins and 15arelative to manifold 8 can now be explained. All of the parts enumeratedare clamped tightly between the shoulder 31 of bushing 29 and the lowershoulder 3 of "adaptor 1, with spacer spring 6 taking up any slack thatmight accumulate in assembly of these parts due to the machiningtolerances required. The longitudinal space in slots 16 and 16a permitslimited longitudinal movement of manifold 8 toadjust to position withrespect to'cylinder 13 and spacer spring 6 in taking up slack asdescribed. 7

Manifold 8 also acts as a sealing head for cylinder 13. By useof thisconstruction, including spacer spring 6, the need for, machining aspecial spacer for each hammer drill is eliminated so that drill partsare interchange- 'ableJ Furthermore, the upper surfaces of manifold 8are always subject to fluid pressure which is higher at all times thanthe fluid pressure on the lower side of the manifold andthe area of thesurfaces on the upper side of manifold 8 which is exposed to such higherfluid pres-' sure is also larger so thata downward thrust is maintainedat all times on the assembled parts. In addition to the fluid pressureholding these parts clamped tightly down against shoulder 31 ofbushing29 the parts are assembled with an initial pressure loading againstspacer spring 6.: With this downward thrust maintained at all times anychance of these parts moving up and down during high speed, highpressure operation and peening their ends is eliminated. i

It is apparent that cylinder 13, liners 26 and 28, lower valve ring 27and annular members 17 19 and 22 could be made integral with housing 5,the inside of the housing being bored to the several internal diametersand shoulders as required. The equivalent construction shown is moreconvenient to manufaeturebecause the housing 5 can be bored with asingleinternal diameter. The separate parts 27, 13, 17, 22, 26 and 28 aremore. easily finished separately to closedimensions andto better surfacefinish, and they provide the necessaryshouldersor differences indiameter for assembly. In addition any of these smaller parts may easilybe replaced if they become worn.

Cylinder 13 has a shoulder 32 on its external circumference, cylinder 13being of such diameter below shoulder 32 as to fit snugly within housing5 and above shoulder 32 being of a reduced diameter such as to permitpassage of drilling fluid through annular space 13a between housing 5and the outer surface of cylinder 13. Immediately above shoulder 32,cylinder 13 is provided with a seriesof ports 33 spaced about itscircumference.

By means of these ports downwardly flowing drilling fluid is permittedto pass from space 13a outside of cylinder 13 to its interior. Aboveports 33 are lugs 34 of which there are three or more circumferentiallyspaced equi-distant from each other and welded to the outer surface ofcylinder 13 to hold it concentric within housing 5 but permitting fluidto flow freely between the lugs. Lugs 34 fit snugly within housing 5sliding freely on the inner surface of the latter during assembly and/or adjustment of the parts against the tension of spacer spring 6,similarly to lugs 14. j 7

Within cylinder 13 immediately above ports 33 and opposite lugs 34 is aconstriction comprising an upper valve ring 35 seated between upper andlower shoulders 36 and 37 in the inner surface of cylinder 13 andforming a sliding seal about outer hammer 40. x 4

Upper valve ring 35 is non-moving and is essentially a part ofcylinder'13.. While it is shown in Figure 1 as a separate element itwill be understood that it may be made integral with cylinder 13. It isadvantageously made and inserted as a separate element in order that itmay be more easily replaced as it is subject to wear from slidingcontact with outer hammer 40 during the high-speed reciprocatingmovement of the latter while the hammer drill is in operation. Also itwill be noted that upper valve ring 35 constitutes the lower end of thestructure comprising outer cylinder 77 as shown in the schematicdrawings 3 to 9 inclusive defining outer cylinder chamber 24.

Outer hammer 40 is an elongate hollow, substantially cylindricallyshaped element provided with by-pass' ports 41 which are spaced aboutthe circumference of hammer 40 immediately adjacent its upper end and ashort distance below by-pas's ports 41' are upper ports 42 which arealso spaced about the circumference of hammer 40. Between ports 41 and42, on the inner circumference of hammer 40 is a sealing ring 38seatedat its lower end in a shoulder 39 in the inner surface of hammer 40 andforming a sliding seal about inner hammer 44-.

The wall thickness of outer hammer 49 is uniform through its centralportion, which wall thickness continues upward to shoulder 39 on theinner. surface of the hammer. From shoulder 39 upward to the upper endof the hammer the wall thickness of the hammer is decreased by thedimension of the shoulder. 38 is essentially a part of outer hammer 40'.It will be understood that while it is shown as a separate element inFigure 1 it may be made an integral part of'outer hammer 40. Like uppervalve ring 35, it is advanta V geously constructed as a separate elementin order to be more easily replaceable as it is subject to wear in thereciprocating movement of the hammers.

Ports 33 in cylinder 13 afford access between passage 13a and an annularshaped upper housing chamber 52 which is situated below ports 33 withinthe lower portion of cylinder 13. Below ports 33 cylinder 13 is ofenlarged diameter and constitutes a liner, fitting snugly within Sealingring E I a As has been stated, the wall thickness of outer hamliner 4%is uniform through the central portion of the hammer. This uniform wallthickness is continued downward to a point just above the lower ports53. At this point the wall thickness of hammer 41? is decreased by asmall amount on its inner surface thereby providing a narrow, downwardlyfacing shoulder 71, the purpose of which will be discussed later. Thedecreased wall thickness of hammer 4%} is continued from shoulder 71 tothe lower end of the hammer. Below lower valve ring 27 an annular shapedlower housing chamber 55 is defined by the valve ring 27, liner 28, theouter surface of outer hammer 4 9, the outer surface of anvil 47 and theupper end of bit stem 67 including split ring 57 sealing bit stem 67 toliner 28. It will be noted that chamber 55 is always open to the outsideof the drill housing by way of passages 56, 50, 51, 63 and 64.

Starting now at the lower end of Figure 2 there is shown a bit stem 67which has a central passage 51 through which drilling fluid reaches thebit. A conventional drilling bit 65 may be screwed into the bit stem 67by means of threads 62. The drill bit 65 has a central passage 63 and isfurther provided with jetting passages 64 connecting the central passagewith the well bore to facilitate the removal of cuttings and chipstherefrom by means of flushing action of the drilling fluid. While afish-tail type of bit is shown the drill bit per se forms no part of myinvention and any type of bit may be used, including rock bits havingrolling cutters. The bit stem 67 is hexagonally shaped and the bushing29 is hexagonally shaped internally to match the shape of the bit stemso that torque may be transmitted from the bushing 29 to the bit stemand bit. Instead of using hexagonally shaped facings on the bushing andbit stem, square or other equivalent shapes may be used or the rotarydriving engagement between bushing 29 and bit stem 67 may beaccomplished by grooves in the bushing and mating splines on the bitstem which engage the grooves.

Accordingly, during drilling the entire assembly may be rotated from thesurface of the ground by means of a conventional drill string (notshown) and this will rotate the bit 65. The bit stem 67 fits slidablywithin bushing 29 permitting a limited amount of longitudinal movement.The upper end of bit stem 67 extends above bushing 29 and is providedwith a split ring 57 rigidly mounted in groove 58. Split ring 57 isslidably sealed to the inner surface of liner 23. The downward movementof bit stem 67 is limited by split ring 57 so that when bit stem 67 isin its lowermost position, split ring 57 abuts against shoulder 31 ofbushing 29. The upward movement of bit stem 67 is also limited, so thatwhen it is in its uppermost position the split ring 57 abuts against ashoulder 59 within liner 28 and external shoulder 76 on the lower end ofbit stem 67 abuts against the lower end of bushing 29.

Inner hammer 44 is a substantially cylindrical member longitudinallypositioned concentrically within outer hammer 40 and is provided with acentral passage 49 which is of increased internal diameter within itsupper end as at 48. The increased internal diameter of passage 49 at 43is in order to accommodate boss 18 at the limit of the upward motion ofinner hammer 44 and at the same time to permit the escape of entrappeddrilling fluid in a dash-pot type of operation, to avoid hydraulichammer. The external diameter of inner hammer 44 at its upper end issuch that it fits closely within sealing ring 33 of outer hammer 40. Ashort distance below the upper end of inner hammer 44 the externaldiameter is decreased, providing a narrow downwardly facing shoulder 79,the purpose of which will be explained later. The portion of hammer 44of decreased external diameter continues downward from shoulder 79 toshoulder 69. At shoulder 69 the external diameter of hammer 44 issubstantially increased so that inner hammer 44 forms a snug sliding fitwithin outer hammer 40. The portion of inner hammer 44 which is ofincreased external diameter extends from shoulder 69 downward toshoulder 72 where the exterior diameter is decreased to approximatelythe same dimension as that portion of the hammer, above described,between shoulders 69 and 76. The reduction in external diameter ofhammer 44 extends downward from shoulder 72 to a point a short distanceabove the upper end of anvil 47 when inner hammer 44 is in its lowermostposition relative to the anvil, as shown in Figure 2. At this point theexternal diameter of hammer 44 is still further reduced to form adownwardly facing shoulder 78 on the outer surface of hammer 44. Thisreduction in external diameter extends downward from shoulder 75 to thelower end of hammer 44. This last described reduction in externaldiameter of hammer 44 serves to conveniently fit hammer 44 within anvil47. The function of shoulders 69 and 72 will be explained later.

The variations in external diameter of inner hammer 44 create twoelongate annular spaces between the inner and outer hammers which aredesignated as upper and lower fluid course chambers, the functions ofwhich will be explained. Upper fluid course chamber 43 is defined byshoulders 69 and 70 and the outer surface of hammer 44 between them andthe inner surface of hammer 4% from a lower point adjacent shoulder 69on the inner hammer to the shoulder 75 formed by the lower side ofsealing ring 38 where it abuts shoulder 39 in outer hammer 4i), andincluding that portion of the inner periphery of outer hammer providedwith upper ports 42. Lower fluid course chamber 54 is defined by theouter surface of inner hammer 44 from shoulder 72 downward to the upperend of anvil 47 which abuts hammer 44, and the inner surface of outerhammer 46 from a point adjacent shoulder 72. on the inner hammer,downward to a point adjacent the upper end of anvil 47 which also abutshammer 40, including that portion of the inner periphery of outer hammer40 provided with lower ports 53 and shoulder 71, and the upper end ofanvil 47. It will be understood that during the reciprocating motion ofthe hammers those portions of the inner surface of outer hammer 40 whichdefine portions of upper and lower fluid course chambers 43 and 54 willvary. Also when the inner hammer is elevated with respect to the outerhammer, as shown in Figures 7 and 8, sealing ring 38 is not in contactwith the outer surface of the inner hammer but forms a narrow passage 74between the ring 38 and the surface of inner hammer 44 where it is ofreduced diameter below shoulder 70.

Anvil 47 is an elongated substantially cylindrically shaped element witha longitudinal passage 50 through the center. Anvil 47 is positionedconcentrically within housing 5, below and in the path of hammers 4t and44 and extends upward between them above the highest point of upwardmovement of the lower end of either of the hammers. At its upper end theanvil 47 forms a close sliding fit between the inner and outer hammers44 and 40 respectively and serves as a guide to direct the verticalreciproeating movement of the hammers to their respective seats. Theexternal diameter of anvil 47 is increased at a point below its upperend providing a shoulder 45 on which outer hammer 49 seats and deliversits percussive blows. The outer surface of anvil 47 is recessed fromshoulder 45 upward to a point, 79, above the highest point of elevationof the lower end of outer hammer 40, in order to provide clearance forany peening which may develop on the lower end of hammer 40 duringoperation. The width of shoul der 45 is therefore slightly greater thanthe wall thickness of outer hammer 40 at this point. Hammer 40 above andanvil 47 below present a uniform exterior diameter. The.- increasedexternal diameter of anvil 47 continues downward to the point at whichit abuts the upper end of bit stem 67. At this point the exteriordiameter of anvil 47" is reduced as at 60 to form a sliding fit withinbit stem 67,

the reduction in diameter providing a downwardly facing shoulder 61 onthe exterior surface of anvil 47 which abuts 7 the upper end of the bitstem 67. The internal diameter of anvil- 47' is increased at a pointbelow its upper end to provide a shoulder 46 on which inner hammer 44seats and delivers its. percussive blows. The'inner surface of anvil. 47is recessed from shoulder 46 upward to a point,

' 80, above thehighest' point of elevation of the lower end of innerhammer 44, in order to provide clearance for any peening which maydevelop on the lower end of inner hammer 44 during operation. Shoulder46 is therefore slightly greater in width than the wall thickness ofthat portion of inner hammer 44- 'adjacent anvil 47. The interiorsurface. of inner hammer 44; and anvil 47 which constitutepassages 49'and 50 respectively are of uniform internal diameter. Inner hammer 44seats on and delivers its percussive blows to' shoulder 46. Shoulders4-5 and 46 therefore constitute anvilfaces. The lower end'of the anvilis seated on a shoulder 66 in the interior surface of bit stem67.Central passage 5% within anvil 7 is in register with centralpassage .49of inner hammer 44 and with central passage 51 of bit stern 67'all beingof the same internal diameterand' forming a continuous smooth surfacedconduit. Passage. 51 in turn connects with passages 63 and 64 of bit 65,and through these is connected to the outside of housing 5.

' A short distance below the top of outer hammer 40 there are provided aseries. of by-pass ports 41. When outer hammer ti'is in its lowermostposition it still partialiy penetrates outer cylinder 77 as shown inFigure 3 and the tip of its upper end is still. within upper valve ring35 but ports f. are not covered by the ring. This permits drilling fluidto be circulated through the drill without activating the hammers. Thepurpose of this is to permit drilling-off (as will be described in moredetail later), and to facilitate drilling-in by permitting the drill tobe run into or out of the bore hole with the drill rotating and withfluid flowing through the drill assembly but without activatingthehammer mechanism. When hy-pass ports 41 are above upper valve ring '35the free circulation of drilling fluid through the drill assembly is cut01f; fluid pressure begins to build up and the hammer mechanism becomesactivated by the increased fluid pressure. However, once the hammermechanism has been started its continuous operation assures anuninterrupted flow of fluid through the drill. a

While the length of the various elements of my drill 1 are notconveniently indicated in Figures 1 and 2 of the accompanying drawings,it is believed clear to those skilled in the art that the length ofinner hammer 44- and outer hammer 49 may be made such as to provide thenecessary mass for these parts and that the length of other parts may beadjusted accordingly. When the bit stem 67 is in its lowermost position,i. e. with split ring 57 resting on shoulder 31 of bushing 29, anvil 47resting in turn.

on shoulders 61 and 66 and hammers 4d and 44 resting on anvil faces 45and 46 the lengths of the parts are made so that the top of outer hammer4i} penetrates upper valve ring 35 a short distance but leaving by-passports 41 fully uncovered.

The operation of my above-described drill will now be explained.Reference is made to the diagrams of Figures 3 to '9 showing the variousphases during the operation of my drill andin which diagrams thenumerals indicate the same elements as in Figures 1 and 2 previouslydescribed. i a

The entire unit will be suspended vertically in the well bore withordinary rotary drill string (not shown) attached to adaptor 1, meansbeing provided at the surface for supplying drilling fluid underpressure to the central passage of the drill string as is well known inthe art. Starting with the drill bit 65 several feet above the bottomof'the hole, bit stem 67 and the other parts will be in their lowermostpositions as described above. The configuration of parts will be asshown in Figure 3.

It is usually desirable to rotate in when a new bit has been. attachedto the drill in order to insure that the bore 8 hole is to gauge, and.to flush out sediment and cuttings which may have settled to the bottomof the hole While the drill pipe wasout of the hole to change bits. Thisis accomplished by establishing circulation of drilling fluid downwardthrough the central passage of the drill pipe and rotating the bit as itis lowered through the last few feet to the botttom of the well borerDuring this rotating in process drilling fluid will be circulatedthrough the drill, using by-pass ports 41, and returning up the holeoutside'of the drill housing 5. Thus hammering will not take place toendanger the drill pipe or other parts as a the drill is lowered intothe hole.

'With the unit suspended in the well bore the weight of the hammers 40and 44 and the weight of the anvil 47' plus. the weight of the bit 6Sand bit stem 67 will force, all of these parts downward to theirlowermost position as shown in Figure 3. In this position split ring 57on the bit stem comes in contact with the upper shoulder 31 of bushing29, and by-pass ports 41 at the upper end of outer hammer 40 are belowupper valve ring 35. Drilling fluid flowing down through the drill,string enters the adaptor through the central passage 2 therein, passesthrough the open center of spacer spring 6 to manifold 8 into upperhousing chamber 52. The fluid'is free to flow through by-pass ports 41in outer hammer into outer cylinder chamber 24, down central passages49, 50 and 51 of inner hammer, anvil and bit stem and out of the drillthrough central passage 63 and jetting holes64 in bit 65. Thus the freeflow of fluid is maintained for flushing out the Well bore. The upperfluid course chamber 43' is open to upper housing chamber 52 via upperports 42 in outer hammer 44). The lower fluid course chamber 54 is open,via lower ports 53 in outer hammer 40, to lower housing chamber 55,which in turn is always open to the outside of the drill throughpassages 56, 50, 51, 63, and 64. Thus all chambers are in openconnection and fluid pressures are substantially the same throughout.

Upon continuing to lower and rotate the mechanism,

including hit stem 67 and bit 65, the nose or cutting edge of the bitwill eventually touch the bottom of the hole. Further lowering of thedrill pipe and attached parts will then cause changes in thelongitudinal position. of housing 5 and the parts carried thereonrelative to the internal parts 67, 47, 40 and 44. With the drill bitresting on bottom, the housing 5 with bushing 29 attached continuesdownward until the lower end of bushing 2? rests on external bit stemshoulder 76 as shown in Figure4.

It will-be noted that in the diagrammatic representations comprisingFigures 3 through 9 inclusive, the outer cylinder-designated by thenumeral 77 is composed of several parts which are shown as separateelements in Figure 1;-namely, annular members 17, 19 and 22 at the top,upper valve ring 35 at the bottom and the wall of i cylinder 13 betweenthese parts joining the elements into '46, andshoulders 69, and 72 oninner hammer 44 can now be described. These shoulders present surfaceswhich are acted upon by the pressure drilling fluid introducedintermittently, by valving action, into the upper and lower fluid coursechambers of the drill through upper and lower ports 52 and 53 therebyproducing reciprocating motion of the hammers as will be explained.Shoulders 71, 75, 6?, 7i and 72 therefore constitute primary andsecondary lifting areas, and down driving areas on the respectivehammers and they are so designated hereinafter. Area 73 on the upper endof outer hammer 40 is also a down driving area and is designated assuch.

a After the drill bit contacts the bottom of the bore hole, continuedlowering of the drill string with attached hous ing and the non-movingparts of the drill contained therein, including upper valve ring 35,moves these elements downward with respect to bit 65 and the othermoving parts of the hammer drill mechanism, namely, bit stem 67, anvil47 and hammers 40 and 44, so that by-pass ports 41 in outer hammer 40are closed off by upper valve ring 35 which is fixed within cylinder 13in housing 5, thus interrupting the free flow of fluid through thedr'dl. The parts will then be essentially in the position as showndiagrammatically in Figure 4. Due to the fact that there is no immediateoutlet for the fluid being supplied under pressure from the surface ofthe ground, fluid pressure will build up within annular passage 2,manifold 3, through ports 10, annular space 13a and ports 33 into upperhousing chamber 52 and through upper ports 42 in outer hammer 40 intoupper fluid course chamber 43 between the inner and outer hammers. Theincreased fluid pressure acts simultaneously on both hammers. The forceexerted by the fluid pressure on primary lifting area 75 of outer hammer40 starts it moving upward. A force is also exerted by the fluidpressure acting on primary lifting area 70 of inner hammer 44. Howeverthe force exerted on primary lifting area 70 is more thancounterbalanced by the downward force exerted by the fluid on downdriving area 69 of inner hammer 44, holding hammer 44 down on the anvil.

When the outer hammer 40 has been raised to a point where lower valvering 27 has closed lower ports 53 in outer hammer 40 from lower housingchamber 55 and slightly opened lower ports 53 to upper housing chamber52, fluid pressure is transmitted from chamber 52 through ports 53 intolower fluid course chamber 54 between the inner and outer hammers. Whenfluid pressure is transmitted into lower fluid course chamber 54 it actson secondary lifting area 71 of outer hammer 49 boosting its upwardmotion. This fluid pressure also acts on the secondary lifting area 72of inner hammer 44 exerting a force which is equal to or slightly largerthan that exerted on down driving area 69 of inner hammer 44, wherebythe downward force on inner hammer 44, (previously holding it down onthe anvil) is cancelled. This leaves the force exerted on primarylifting area 70 the only effective force being exerted on inner hammer44, so that hammer 44 then starts to move upward. Fluid displaced by theupward-moving inner hammer 44 in cylinder chamber 24 escapes throughcentral passage 49 in inner hammer 44 which is always open via passages50, 51, 63 and the bit jetting holes 64 to the lower pressure outside ofthe drill. This stage of the operation is illustrated in Figure 5 of theschematic drawings.

The overlap of operation of upper and lower ports 42 and 53 determinesthe location of outer hammer 4%) when inner hammer 44 starts upward, andalso regulates the speed and impact of the outer hammer on its downwardtravel. The amount of overlap depends on the location of lower valvering 27 which can be adjusted by means of different spacer lengths inthe finished drill.

At the start of operation of the hammer mechanism, inner hammer 44 isheld down against anvil seat 46 while outer hammer 40 starts movingupward under the impetus of fluid pressure. After outer hammer 40 ismoving upward, inner hammer 44 starts its upward travel as describedabove. When outer hammer 40 approaches its maximum elevation, innerhammer 44 is entering inner cylinder 20 sealing off inner cylinderchamber 23 from outer cylinder chamber 24 and thereby sealing off theescape of fluid from chamber 24 (by means of passage 49 in inner hammer44. Fluid entrapped in outer cylinder chamber 24 acts as a hydraulicstop for the upward movement of outer hammer 40.

As inner hammer 44 continues its upward stroke to maximum elevation,fluid is also entrapped by it in annular space 21 between annular member20 and boss 13, and acts as a hydraulic stop for the upward movement ofinner hammer 44. This operation will be dev 16 scribed in more detailbelo It will be understood that outer cylinder chamber 24 of Figure 6 isthe same as chamber 24 in Figure l which is defined at its upper end byannular member 22, at its lower end by upper valve ring 35 and on itsouter periphery by cylinder 13.

As shown in Figure 6, upper ports 42 are closed to upper housing chamber52 and open to outer cylinder chamber 24 connecting chamber 24 withupper fluid course chamber 43 between the inner and outer hammers. Innerhammer 44 continues to travel upward, under the pressure transmittedthrough lower ports 53 and acting on secondary lifting area 72 of innerhammer 44. This upward movement of inner hammer 44 displaces fluid fromupper fluid course chamber 43 which moves out through upper ports 42into outer cylinder chamber 24 and there exerts force on the top area 73of outer hammer 40 driving it downward. Fluid displaced in lower housingchamber 55 by the lower end of outer hammer 40 moving downward escapesthrough anvil passages 56 and 50 and bit stem passage 51 which, asstated, are always open to the lower pressure outside of the drill.

As shown in Figure 7, when inner hammer 44 reaches its maximum elevationit engages boss 13 forming annular chamber 21 in which fluid is trapped.However, the internal diameter of the longitudinal passage 49 throughinner hammer 44 is increased as at 48 so that fluid trapped in chamber21 can escape between the boss and the inner circumference of the hammerdown passage 49 in hammer 44. Thus chamber 21 and boss 18 function as adashpot for hammer 44 and stop its upward movement gradually, operatingas a hydraulic cylinder, thereby avoiding a sudden stop and resultinghydraulic hammer. At this point outer hammer 40 has moved downwardsufliciently so that upper ports 42 are below upper valve ring 3:;opening upper fluid course chamber 43 to high fluid pressure from upperhousing chamber 52. Also sealing ring 38 of outer hammer 453 is nolonger sealed to the outer surface of inner hammer 44 but faces upperfluid course chamber 43 forming a passage 74 between sealing ring 38 andinner hammer 44. High fluid pressure is therefore transmitted from upperhousing chamber 52 through ports 42 into upper fluid course chamber 43,through passage 74 and into outer cylinder chamber 24 where it exerts aforce on the top area 73 of outer hammer 4t) accelerating its downwardmovement. Lower ports 53 are almost closed to upper housing chamber 52and when closed upward pressure on secondary lifting area 71 of outerhammer 4t} and secondary lifting area 72 of inner hammer 44 will be cutoff.

When outer hammer 4i) delivers its blow to anvil face 45 inner hammer 44is moving downward under the impetus of fluid pressure on downwarddriving area 69 exerted through upper ports 42 and upper fluid coursechamber 43. Fluid displaced in lower fluid course chamber 54 by thelower end of inner hammer 44 moving downward escapes through lower ports53, which are open at this point to lower housing chamber 55. As shownin Figure 8 of the drawings, at this stage of the operation inner hammer44 is moving downward, leaving inner cylinder 2%), and sealing ring 33of outer hammer 41) is seating against inner hammer 44 closing passage74. With passage 74 closed, fluid pressure is exerted on primary liftingarea 75 of outer hammer 4% to start it moving upward again on its nextstroke.

After outer hammer 4G delivers its blow to anvil face 45 and startsupward for its next stroke, inner hammer 44 delivers its blow to anvilface 46. Although outer hammer 49 is moving upward, lower ports 53 arestill open to lower housing chamber 55 which, as has been pointed out,is always open to the outside of the drill housing by way of passages56, 5t), 51, 63 and 64, so that no fluid pressure is exerted onsecondary lifting area 72 of inner hammer 4-4. A downward force isexerted by the fluid pressure acting through upper ports 42 on downdriving area 69 of inner hammer 44 holding it down on 11 anvil face 46.This stage of the operation of the drill is illustrated in Figure 9 ofthe diagrammatic drawings.

This completes the operating cycle. which starts over again beginning asshown in Figure 5. It will be noted that after the drill action starts,both hammers are never in contact with the anvil at the same time andare always moving relative to each other, thereby maintaining anuninterrupted flow of drilling fluid. In the operation of this hammerdrill an operating speed of six hundred cycles per minute was achieved,making a total of twelve hundred blows per minute delivered to the anvilby the hammers.

-While the above described hammer represents a preferred'embodiment ofmy invention an alternative type of construction may be used in whicheither hammer constitutes the sole effective percussive element and theother hammer acts only as a valving element. In such an alternativeembodiment of my invention the hammer constituting the valv'ing elementwould be of much lighter construction. For example, it could be made ofmuch lesser wall thickness, or of a lighter material such as aluminum,or both.

As previously stated, my hammer drill is not limited to operation in avertical position, since it is not dependent on the force of gravity toassist the hammers in imparting percussive blows to the anvil. In thedescription of the parts of mydrill both in this specification and inthe appended claims the terms up, down, above, below, upwardly,downwardly, etc., have been used in a relative sense, that is, the wordsup, above, and upwardly refer to a direction toward adaptor 1 from whichthe pressurized operating fluid flows, while below, down, and downwardlyrefer to a direction toward the bit stem and bit at the opposite end ofthe hammer drill assembly, i. e. the direction in which the pressurizedoperating fluid is discharged.

It will be apparent that other modifications and variations may be madein the above described structure and its method of operation, withoutdeparting from the scope and spirit of the present invention, thereforeonly such limitations should be imposed as are indicated in the appendedclaims.

I claim:

l. A fluid operated positive displacement type hammer mechanismcomprising a tubular housing, an elongate hollow outer hammer providedwith upper and lower ports therein adjacent the respective upper andlower ends thereof, said outer hammer being longitudinally disposedwithin said housing, an elongate inner hammer longitudinally disposedwithin and slidably sealed to the inner surface of said outer hammer,said inner hammer being provided with a longitudinal passagetherethrough, a cylinder closed at its upper end disposed within theupper end of said housing and with the upper ends of said'hammersextending within said cylinder, an anvil disposed within said housingbelow and in the path of said harnmers, said anvil being provided with alongitudinal passage therethrough in register with the passage in saidinner hammer, a constriction within said cylinder slidably sealed aboutthe upper end of said outer hammer, a constriction within said housingslidably sealed about the lower end of said outer hammer, meansintroducing pressurized operating fluid into said housing below saidcylinder, an upper fluid course chamber formed between the upper portionof the inner hammer and the upper portion of the outer hammer, saidupper fluid course chamber being adapted to cooperate with said upperports in said outer hammer and said constriction in said cylinder toeflect longitudinal reciprocating movement of said inner and outerhammers under the force of the pressurized operating fluid, a lowerfluid course chamber formed between the lower portion of the innerhammer and the lower portion of the outer hammer, said lower fluidcourse chamber being adapted to cooperate with said lower ports in saidouter hammer and said constriction in said housing to assist ineffecting 12 longitudinal reciprocating movement of said inner and outerhammers under the force of the pressurized operat-' ing fluid. 2. Afluid operated positive displacement type hammer mechanism comprising atubular housing, an elongate hollow outer hammer positionedlongitudinally within said housing, said outer hammer being providedwith upper and lower ports adjacent the respective upper and lower endsthereof and being adapted for longitudinal reciproeating movement, anelongate inner hammer provided with a longitudinal passage therethrough,said inner hammer being longitudinally disposed within and slidablysealed to the inner surface of said outer hammer and adapted forlongitudinal reciprocating movement, a cylin der closed at its upper enddisposed within the upper end of said housing and with the upper ends ofsaid hammers extending within said cylinder, an anvil disposed withinsaid housing below and in the path of said hammers, said anvil beingprovided with faces for seating said inner and outer hammers and forreceiving percussive blows therefrom and being provided with alongitudinal passage therethrough in register with the longitudinalpassage in said inner hammer, a constriction within said cylinderslidably sealed about the upper end of said outerrha mmer adjacent theupper ports therein, a constriction in said housing slidably sealedabout the lower end of said outer hammer adjacent the lower portstherein, means introducing pressurized operating fluid into said housingbelow the lower end of said cylinder and affording said pressurizedoperating fluid intermittentaccess to the upper and lower ports in saidouter hammer, an upper fluid course chamber formed between the upperportion of the inner hammer and the upper portion of the outer hammer, alower fluid course chamber formed between the lower portion of the innerhammer and the lower portion of the outer hammer, said upper fluidcourse chamber being adapted to cooperate with said upper ports in saidouter hammer and said constriction in said cylinder to effectlongitudinal reciprocating movement of said' inner and V outer hammersunder the force of the pressurized operat,

ing fluid, said lower fluid course chamber being adapted to cooperatewith said lower ports in said outer hammer and said constriction in saidhousing to assist in effecting longitudinal reciprocating movement ofsaid inner and outer hammers under the force of the pressurizedoperating fluid.

3. A fluid operated positive displacement type hammer mechanismcomprising a tubular housing, an elongate hollow outer hammer providedwith upper and lower ports adjacent the respective upper and lower endsthereof, said outer hammer being disposed longitudinally within saidhousi g, n elongate inner hammer longitudinally disposed within andslidably sealed to the inner surface of said outer hammer and providedwith a longitudinal passage. therethrough, a cylinder closed at-itsupper end disposed within the upper end of said housing and withtheupper ends of said hammers extending within said. cylinder, a downwardlyprojecting annular boss and a downwardly extending annular flangesurrounding said boss disposed within the upper end of said cylinder, ananvil disposed within said housing below and in the path of saidhammers, said anvil being provided with a longitudinal passagetherethrough in register with the longitudinal passage in said innerhammer, a constriction within said cylinder slidably sealed about theupper end of said outer hammer adjacent the upper ports therein, aconstriction within said housing slidably sealed about the lower end ofsaid outer hammer adjacent the lower ports therein, means introducingpressurized operating fluid into said housing below said cylinder, anupper fluid course chamber formed between the upper portion of the innerhammer and the upper portion of the outer hammer, a lower fluid coursechamber formed between the lower portion of the inner hammer and thelower portion of the outer hammer, said upper fluid course chamber beingadapted to cooperate V 1a with said upper ports in said outer hammer andsaid constriction in said cylinder to effect longitudinal reciprocatingmovement of said inner and outer hammers under the force of thepressurized operating fluid, said lower fluid course chamber beingadapted to cooperate with said lower ports in said outer hammer and saidconstriction in said housing to assist in effecting longitudinalreciprocating movement of said inner and outer hammers under the forceof the pressurized operating fluid, said reciprocating movement of saidouter hammer being substantially between an upper position defined byclosure of said upper ports in said outer hammer by said constriction insaid cylinder and a lower position contacting said anvil, and saidreciprocating movement of said inner hammer being substantially betweenan upper position defined by engagement of the upper end of said innerhammer with said downwardly projecting boss and annular flangesurrounding said boss within the upper end of said cylinder and a lowerposition contacting said anvil.

4. A fluid operated positive displacement type hammer mechanismcomprising a tubular housing, inner and outer hammers longitudinallydisposed within said housing and adapted for longitudinal reciprocatingmovement, said outer hammer comprising an elongate hollow elementprovided with upper and lower ports therein adjacent the respectiveupper and lower ends thereof, said inner hammer comprising an elongateelement longitudinally disposed within and slidably sealed to the innersurface of said outer hammer and being provided with a longitudinalpassage therethrough, a cylinder closed at its upper end disposed withinthe upper end of said housing and with the upper ends of said hammersextending within said cylinder, a downwardly projecting annular boss anda downwardly extending annular flange surrounding said boss disposedwithin the upper end of said cylinder, an anvil disposed within saidhousing below and in the path of said hammers, said anvil being providedwith faces for seating said inner and outer hammers and for receivingpercussive blows therefrom and being provided with a longitudinalpassage therethrough in register with the longitudinal passage in saidinner hammer, a constriction within said cylinder slidably sealed aboutthe upper end of said outer hammer adjacent the upper ports therein, aconstriction within said housing slidably sealed about the lower end ofsaid outer hammer adjacent the lower ports therein, means introducingpressurized operating fluid into said housing below said cylinder,shoulders on the outer surface of said inner hammer adjacent the upperend thereof cooperating with a shoulder on the inner surface of saidouter hammer adjacent the upper end thereof to form an upper fluidcourse chamber adapted to receive a flow of said pressurized operatingfluid, said upper ports in said outer hammer cooperating with saidconstriction in said cylinder to intermittently interrupt said flow ofpressurized operating fluid to said upper fluid course chamber toefliect longitudinal reciprocating movement of said inner and outerhammers, a shoulder on the outer surface of said inner hammer adjacentthe lower end thereof cooperating with a shoulder on the inner surfaceof said outer hammer adjacent the lower end thereof and said anvil toform a lower fluid course chamber adapted to receive a flow of saidpressurized operating fluid, said lower ports in said outer hammercooperating with said constriction in said housing to intermittentlyinterrupt said flow of pressurized operating fluid to said lower fluidcourse chamber to assist the operation of said upper fluid coursechamber in effecting longitudinal reciprocating movement of said innerand outer hammers, said reciprocating movement of said outer hammerbeing substantially between an upper position defined by closure of saidupper ports in said outer hammer by said constriction in said cylinderand a lower position contacting said anvil, and said reciprocatingmovement of said inner hammer being substantially between an upperposition defined by engagement of the t v l4 upper end of said innerhammer with said downwardly projecting boss and said annular flangesurrounding said boss within the upper end of said cylinder and a lowerposition contacting said anvil.

5. A fluid operated positive displacement type hammer drill comprising atubular housing, an elongate hollow outer hammer provided with upper andlower ports therein adjacent the respective upper and lower endsthereof, said outer hammer being disposed longitudinally within saidhousing, an elongate inner hammer longitudinally disposed within andslidably sealed to the inner surface of said outer hammer and providedwith a longitudinal passage therethrough, a cylinder closed at its upperend disposed within the upper end of said housing and with the upperends of said hammers extending within said cylinder, a downwardlyprojecting annular boss and a downwardly extending annular flangesurrounding said boss disposed within the upper end of said cylinder, ananvil disposed within said housing below and in the path of saidhammers, said anvil being provided with faces for seating said inner andouter hammers and for receiving percussive blows therefrom and beingprovided with a longitudinal passage therethrough in register with thelongitudinal passage in said inner hammer, means introducing pressurizedoperating fluid into said housing below said cylinder, a constrictionwithin said cylinder slidably sealed about the upper end of said outerhammer adjacent the upper ports therein, a constriction within saidhousing slidably sealed about the lower end of said outer hammeradjacent the lower ports therein, an upper fluid course chamber formedbetween the upper portion of the inner hammer and the upper portion ofthe outer hammer, a lower fluid course chamber formed between the lowerportion of the inner hammer and the lower portion of the outer hammer,said upper fluid course chamber being adapted to cooperate with saidupper ports in said outer hammer and said constriction in said cylinderto eflect longitudinal reciprocating movement of said inner and outerhammers under the force of the pressurized operating fluid, said lowerfluid course chamber being adapted to cooperate with said lower ports insaid outer hammer and said constriction in said housing to assist inelfecting longitudinal reciprocating movement of said inner and outerhammers under the force of the pressurized operating fluid, saidreciprocating movement of said outer hammer being substantially betweenan upper position defined by closure of said upper ports in said outerhammer by said constriction in said cylinder and a lower positioncontacting said anvil, said reciprocating movement of said inner hammerbeing substantially between an upper position defined by engagement ofthe upper end of said inner hammer with said downwardly projecting bossand annular flange surrounding said boss within the upper end of saidcylinder and a lower position contacting said anvil, and a bit stemslidably sealed within the lower end of said housing below said anvil,said bit stem being adapted for carrying a drilling tool and beingprovided with a longitudinal passage therethrough in register with thelongitudinal passage in said anvil.

6. A fluid operated positive displacement type hammer drill comprising atubular housing an elongate hollow outer hammer provided with upper andlower ports there in adjacent the respective upper and lower endsthereof, said outer hammer being disposed longitudinally within saidhousing, an elongate inner hammer longitudinally disposed within andslidably sealed to the inner surface of said outer hammer and providedwith a longitudinal passage therethrough, said inner hammer beingapproximately equal in length and mass to said outer hammer, a cylinderclosed at its upper end disposed within the upper end of said housingand with the upper ends of said hammers extending within said cylinder,a downwardly projecting annular boss and a downwardly extending annularflange surrounding said boss disposed within the upper end of saidcylinder, a constriction within said cylinder slidably sealed about theupper end of said outer hammer adjacent the upper portstherein,aconstriction within said housing slidably sealed about the lower end ofsaid outer hammer adjacent the lower ports therein, an anvil disposedwithin said housing below and in the path of said hammers, said anvil"being provided with faces for seating'said inner and outer hammers andfor receiving percussive blows therefrom and being provided with alongitudinal passage therethrough in register with the longitudinalpassage in said inner hammer, said anvil also being provided with alateral passageway connecting the longitudinal passage therein with theinterior of said housing below said constriction therein exterior ofsaid anvil and said outer hammer, means introducing pressurizedoperating fluid into said housing below the lower end of said cylinder,an upper fluid course chamber formed between the upper portion of theinner hammer and the upper portion of the outer hammer, a lower of theinner hammer and the lower Portion of the outer hammer, saidconstriction in said cylinder being adapted to cooperate with said upperports in said outer hammer to afford said pressurized operating fluidintermittent access to said upper fluid course chamber toeifectlongitudinal reciprocating movement of said inner and outerhammers, said constriction. in said housing being adapted to cooperatewith said lower ports in said outer hammer to afford said pressurizedoperating fluid intermittent access to said lower fluid course chamberto assist in effecting longitudinal reciprocating movement of said innerand outer hammers,said reciprocating movement of said outer hammer beingsubstantially between an upper position defined by closure of said upperports in said outer hammer by said constriction in said cylinder and alower position contacting said anvil, said reciprocating movement ofsaid inner hammer being substan tially between an upper position definedby engagement of the upper end of said inner hammer with said downwardlyprojecting boss ,and annular flange surrounding said boss within theupper end of said cylinder and a lower position contacting said anvil,and a bit stem slidably sealed within the lower end of said housingbelow said anvil, said bit stem being adapted for carrying a drillingtool and being provided with a longitudinal passage therethrough inregister with the longitudinal passage in said anvil.

7. A fluid operated positive displacement type hammer drill comprising atubular housing, an elongate hollow outer hammer positionedlongitudinally within said housing, said outer hammer being providedwith upper and lower ports adjacent the respective upper and lower endsthereof and being adapted for longitudinal reciprocating movement, anelongate inner hammer provided with a longitudinal passage therethrough,said inner. hammer being disposed longitudinally within and slidablysealed to the inner surface of said outer hammer and adapted forlongitudinal reciprocating movement, a cylinder closed at its upper enddisposed within the upper end of said housing and with the upper ends ofsaid hammers extending within said cylinder, a constriction in saidcylinder slidably sealed about the upper end of said outer hammeradjacent the upper ports therein, a constriction in said housingslidably sealed about the lower end of said outer hammer adjacent thelower ports therein, an anvil disposed within said housing below and inthe path of said hammers, said anvil being provided. with faces forseating said inner and outer hammers and for receiving percussive blowstherefrom and being provided with a longitudinal passage therethrough inregister with the longitudinal passage in said inner hammer said anvilalso being provided with a lateral passageway connecting thelongitudinal passage therein with the interior of said housing belowsaid constriction therein exterior of said anvil and said outer hammer,means introducing V pressurized operating fluid into isaid housing belowthe lower end of said cylinder and aflfording said pressurized operatingfluid intermittent access to the upper and lower ports in said outerhammer, a sealing ring fixedly attached to the inner surface within theupper end'of said outer hammer, said sealing ring being slidably sealedabout the upper end of said inner hammeI the lower side of said sealingring forming a downwardly facing annular shoulder on the inner surfaceof said outer hammer, a narrow downwardly facing annular shoulder on theinner surface of said outer hammer, immediately above said lower portstherein, a narrow downwardly-facing annular shoulder on the outersurface of said inner hammer adjacent the upper end thereof, a widerupwardly facing annular shoulder spaced below said narrow downwardlyfacing shoulder on the outer surface of'said inner harnmer, a centralportion of said inner hammer of increased external diameter slidablysealed to the inner surface of said outer hammer below said upwardlyfacing shoulder on said inner hammer, a downwardly facing annularshoulder below said central portion of said inner hammer at least equalin width to said upwardly facing shoulder, and a bit stem slidablysealed within the lower' end of said housing below said anvil, saidbittstem being provided with a downward extension adapted to carry adrilling tool and being provided with a longitudinal passagetherethrough in register with the longitudinal passage in said anvil, t7 p 8, The apparatus of claim 7 wherein is provided a downwardlyprojecting annular boss and a downwardly extending annular flangesurrounding said boss disposed within the upper end of said' cylinder,said boss and flange being of such' dimensions as to provide adownwardly opening annular space therebetween of suflicient' width toclosely engage said inner hammer at the top of its upward'stroke therebycushioning the termination of the upward movement of said inner hammerand whereby upward movement of said outer hammer, ishydraulicallycushioned upon closure of said upper ports as said outer hammerapproaches maximum elevation on its upward stroke, and fluid pressure isexertedron the ports adjacent its upper end, upper ports adjacent itsupper end below said by-pass ports, and lower ports adjacent its lowerend and being adapted for longitudinal reciprocating movement, anelongate inner hammer approximately equal in length and mass to saidouter hammer and provided with a longitudinal passage therethrough, saidinner hammer being longitudinally disposed withintand slidably sealed tothe inner. surface of said lower end of said outer hammer adjacent thelower ports therein, an anvil disposed within said housing below and inthe path of said hammers, said anvil being provided with faces forseating said inner and outer hammers and for receiving percussive blowstherefrom and being provided with a longitudinal passage therethrough inregister with the longitudinal passage in said innerthammer, said anvilalso being provided Witha lateral passageway connecting the longitudinalpassage therein with the interior of said housing below saidconstriction therein exterior of said anvil and said outer hammer, meansintroducing pressurized o'perating fluid into said housing below thelower end of said cylinder and affording said pressurized operatingfluid intermittent access to said upper and lower ports in said outerhammer, a sealing ring on the inner surface of said outer hammeradjacent the upper end thereof, said sealing ring forming a sliding sealabout the upper end of said inner hammer, an annular shaped upper fluidcourse chamber formed between the upper end of said inner hammer and theupper end of said outer hammer, said upper fluid course chamber beingdefined by a narrow downwardly facing annular shoulder on the outersurface of said inner hammer adjacent the upper end thereof, a widerupwardly facing annular shoulder spaced below said narrow downwardlyfacing shoulder on the outer surface of said inner hammer, the outersurface of said inner hammer between said shoulders, a downwardly facingshoulder formed by the lower side of said sealing ring on the innersurface of said outer hammer adjacent the upper end thereof, and theinner surface of said outer hammer downward from said shoulder to apoint opposite said upwardly facing shoulder on said inner hammer,including that portion of the inner surface of said outer hammer inwhich said upper ports are located, a central portion of said innerhammer of increased external diameter below said last mentioned upwardlyfacing shoulder on said inner hammer slidably sealed to the innersurface of said outer hammer, an annular shaped lower fluid coursechamber formed between the lower end of said inner hammer and the lowerend of said outer hammer below said upper fluid course chamber, saidlower fluid course chamber being defined at its upper end by adownwardly facing annular shoulder on the outer surface of said innerhammer below said central portion of said inner hammer, said downwardlyfacing shoulder being at least equal in width to said upwardly facingshoulder on said inner hammer, said lower fluid course chamber beingdefined at its lower end by the upper end of said anvil, on its innerperiphery by the outer surface of said inner hammer between said lastmentioned downwardly facing shoulder and said anvil, and on its outerperiphery by the inner surface of said outer hammer from a pointopposite said last mentioned downwardly facing shoulder on said innerhammer downward to the upper end of said anvil, including that portionof the inner surface of said outer hammer in which said lower ports arelocated, a narrow downwardly facing shoulder on the inner surface ofsaid outer hammer immediately above said lower ports Within said lowerfluid course chamber, a bit stem slidably sealed within the lower end ofsaid housing below said anvil, said bit stem being adapted to be rotatedby rotation of said housing and being provided with a downward extensionadapted to carry a drilling tool, and a longitudinal passage in said bitstem in register with the longitudinal passage in said anvil.

References Cited in the file of this patent UNITED STATES PATENTS1,110,067 MacDonald Sept. 18, 1914 2,661,928 Topanelian Dec. 8, 19532,673,713 Ringler Mar. 30, 1954 2,714,370 Ieschke Aug. 2, 1955

